The present invention relates to the antiviral compound calcium (3S) tetrahydro-3-furanyl (1S,2R)-3-[[(4-aminophenyl)sulfonyl](isobutyl)amino]-1-benzyl-2-(phosphonooxy)propylcarbamate, pharmaceutical compositions comprising it, its use in the treatment of retroviral infections, and processes for its preparation.
Virus-encoded proteases, which are essential for viral replication, are required for the processing of viral protein precursors. Interference with the processing of protein precursors inhibits the formation of infectious virions. Accordingly, inhibitors of viral proteases may be used to prevent or treat chronic and acute viral infections.
A new antiviral compound, (3S) tetrahydro-3-furanyl (1S,2R)-3-[[(4-aminophenyl)sulfonyl](isobutyl)amino]-1-benzyl-2-(phosphonooxy)propylcarbamate, described in PCT/US98/04595, has HIV aspartyl protease inhibitory activity and is particularly well suited for inhibiting HIV-1 and HIV-2 viruses. Moreover, (3S) tetrahydro-3-furanyl (1S,2R)-3-[[(4-aminophenyl)sulfonyl](isobutyl)amino]-1-benzyl-2-(phosphonooxy)propylcarbamate has increased solubility in the pH range of the gastro-intestinal tract compared to the HIV protease inhibitor [3S-[3R*(1R*,2S*)]]-[3-[[(4-aminophenyl)sulfonyl](2-methyl-propyl)amino]-2-hydroxy-1-phenylmethyl)propyl]-tetrahydro-3-furanyl ester (amprenavir, 141W94). Amprenavir, which has poor solubility and is thus available as a solution in gel capsules and has a high pill burden. This new HIV protease inhibitor with its increased solubility thus has the potential to reduce the perceived pill burden and may be formulated as a tablet.
However, attempts to find a stable crystalline form of (3S) tetrahydro-3-furanyl (1S,2R)-3-[[(4-aminophenyl)sulfonyl](isobutyl)amino]-1-benzyl-2-(phosphonooxy)propylcarbamate suitable for formulation proved problematic. A range of salts of the phosphoric acid were made (for example, di-sodium, di-potassium, magnesium, zinc, ethylene diamine, piperazine). Of these, the piperazine salt was a crystalline solid, but had the practical disadvantage of likely toxicity at the anticipated dose. Surprisingly, we have found that the calcium salt, calcium (3S) tetrahydro-3-furanyl (1S,2R)-3-[[(4-aminophenyl)sulfonyl](isobutyl)amino]-1-benzyl-2-phosphonooxy)propylcarbamate, has a stable crystalline form. Detailed further examination revealed that this salt has advantageous properties making it suitable for formulation into tablets. Thus the compound of the present invention provides an opportunity to reduce the pill burden associated with some HIV protease inhibitors.
The structure of calcium (3S) tetrahydro-3-furanyl (1S,2R)-3-[[(4-aminophenyl)sulfonyl](isobutyl)amino]-1-benzyl-2-(phosphonooxy)propylcarbamate, a compound of formula (I), is shown below: 
We have now found that the compound of formula (I) can be prepared in crystalline form, exhibiting particularly good pharmaceutical properties.
According to a first aspect of the invention there is provided the compound of formula (I) in crystalline form, hereinafter referred to as Form (I).
The invention relates to Form (I) of the compound of formula (I) in crystalline form. Typically, Form (I) contains about 4 to 5 moles of water. However, in any batch containing Form (I) of the compound of formula (I) there may also be other solvated crystalline forms of the compound of formula (I).
Solid State Form (I) of the compound of formula (I) can be characterised by it""s X-ray powder diffraction pattern, shown in FIG. 1. Diffraction traces were obtained using a Phillips PW1800 diffractometer (serial DY701) and Cu K xcex1 radiation. X-ray intensities were measured at 0.02xc2x0 increments for 4 second intervals using a scintillation counter, between values of 2 and 45xc2x0 2xcex8. Intense diffraction peaks characteristic of Form (I) may occur at the following approximate 2theta angles (using copper K xcex1 X-radiation): 5.735, 9.945, 11.500, 13.780, 14.930, 15.225, 17.980, 19.745, 21.575, 22.170, 24.505, and 27.020. Further details are presented in Table 1.
It will be appreciated by those skilled in the art that the compound of formula (I) may be in the form of a solvate, for example a hydrate.
According to a further aspect, the present invention provides a process for the production of the compound of formula (I) in a crystalline form, said process comprising the reaction of a compound of formula (II) 
with a phosphorylating agent, for example phosphorus oxychloride, phosphorus pentachloride, or dibenzylchlorophosphate, in the presence of a base, for example pyridine, triethylamine or diisopropylethylamine, and optionally in the presence of a solvent, for example methylisobutylketone or dichloromethane; followed by reduction, typically of the sodium salt formed in aqueous solution by addition of sodium bicarbonate, sodium carbonate or sodium hydroxide, with a reducing agent, for example formic acid or hydrogen with palladium/ or platinum/carbon catalyst, in the presence of a suitable solvent, for example water, ethyl acetate, isopropanol, acetone, methanol, industrial methylated spirit or a mixture of two or more of the above solvents; followed by the addition of water and a source of calcium ions, for example calcium acetate, calcium chloride or calcium hydroxide, optionally in the presence of an additional solvent selected from the above-mentioned list.
In a further aspect, the present invention also provides a process for the production of the compound of formula (I), comprising dissolving a compound of formula (III) 
in a suitable solvent, for example isopropanol, methanol or industrial methylated spirit, and adding to the solution water and a source of calcium ions, for example calcium acetate, calcium chloride or calcium hydroxide.
In a further aspect, the present invention also provides a process for the production of the compound of formula (I), comprising the reduction of a compound of formula (IV), typically of the sodium salt formed in aqueous solution by addition of sodium bicarbonate, sodium carbonate or sodium hydroxide 
in the presence of a suitable reducing agent, for example formic acid or hydrogen with palladium/ or platinum/carbon catalyst, in the presence of a suitable solvent, for example water, ethyl acetate, isopropanol, acetone, methanol industrial methylated spirit or a mixture of two or more of the above solvents; followed by the addition of water and a source of calcium ions, for example calcium acetate, calcium chloride or calcium hydroxide, optionally in the presence of an additional solvent selected from the above-mentioned list.
It will be appreciated by those skilled in the art that each step may be followed by a standard isolation and purification procedure such as those detailed in the examples hereinafter.
The compound of formula (I) thus obtained may optionally be further purified by recrystallisation from an appropriate solvent, for example industrial methylated spirit, acetone, methanol or isopropanol and mixtures thereof with water, preferably a mixture of industrial methylated spirit and water.
A further optional purification step may be carried out by heating a slurry of the product in water to a temperature in the range 70-99xc2x0 C., preferably 85-97xc2x0 C., most preferably 90-95xc2x0 C., for about 2.5-6 hours, preferably 3-5 hours, most preferably 4 hours, followed by cooling to ambient temperature and harvesting the solid.
The compound of formula (II) may be prepared by any method known in the art, but preferably by the methods described in WO94/05639, incorporated herein by reference hereto.
The compound of formula (III) may be prepared by reaction of a compound of formula (II) with a phosphorylating agent, for example phosphorus oxychloride, phosphorus pentacloride or dibenzylchlorophosphate, in the presence of a base, for example pyridine, triethylamine or diisopropylethylamine, and optionally in the presence of a solvent, for example methylisobutylketone or dichloromethane; followed by reduction, typically of the sodium salt formed in aqueous solution by addition of sodium bicarbonate, sodium carbonate or sodium hydroxide, with a reducing agent, for example formic acid or hydrogen with a palladium/ or platinum/carbon catalyst; in the presence of a suitable solvent, for example water, ethyl acetate, isopropanol, methanol, acetone, industrial methylated spirit or a mixture of two or more of the above solvents.
The compound of formula (IV) may be prepared by the reaction of a compound of formula (II) with a phosphorylating agent, for example phosphorus oxychloride or phosphorus pentachloride, in the presence of a base, for example pyridine, triethylamine or diisopropylethylamine and optionally in the presence of a solvent, for example methylisobutylketone or dichloromethane.
Preferably the phosphorylating agent is phosphorus oxychloride. Preferably the base is pyridine. Preferably the solvent is methyl isobutylketone.
Preferably the reducing agent is hydrogen with a palladium on carbon catalyst with a 5-10% loading of palladium. Preferably the solvent is a mixture of industrial methylated spirit and water
The present invention also provides the compound of formula (I) for use in medical therapy, for example in the treatment of a viral disease in an animal, for example, a human. The compound is especially useful for the treatment of diseases caused by retroviruses, such as HIV infections, for example, Acquired Immune Deficiency Syndrome (AIDS) and AIDS-related complex (ARC) as well as diseases caused by hepatitis B and hepatitis C.
In addition to its use in human medical therapy, the compound of formula (I) can be administered to other animals for treatment of viral diseases, for example to other mammals.
The present invention also provides a method for the treatment of a viral infection, particularly a retrovirus infection such as an HIV infection, in an animal, for example, a mammal such as a human, which comprises administering to the animal an effective antiviral amount of the compound of formula (I).
The present invention also provides the use of the compound of formula (I) in the preparation of a medicament for the treatment of a viral infection, particularly a retrovirus infection such as an HIV infection.
The compound of formula (I), also referred to herein as the active ingredient, may be administered by any route appropriate to the condition to be treated, but the preferred route of administration is oral. It will be appreciated however, that the preferred route may vary with, for example, the condition of the recipient.
For each of the above-indicated utilities and indications the amounts required of the active ingredient (as above defined) will depend upon a number of factors including the severity of the condition to be treated and the identity of the recipient and will ultimately be at the discretion of the attendant physician or veterinarian. In general however, for each of these utilities and indications, a suitable effective dose will be in the range of 0.1 to 150 mg per kilogram body weight of recipient per day, advantageously in the range of 0.5 to 70 mg per kilogram body weight per day, preferably in the range of 0.5 to 50 mg per kilogram body weight per day (unless otherwise indicated, all weights of the active ingredient are calculated with respect to the free base of the compound of formula (I)). The desired dose is preferably presented as one, two, three or four or more subdoses administered at appropriate intervals throughout the day. These sub-doses may be administered in unit dosage forms, for example, containing about 25 to 2000 mg, preferably about 50, 100, 150, 200, 250, 300, 450, 500, 570, 750 or 1000 mg of active ingredient per unit dose form.
While it is possible for the active ingredient to be administered alone, it is preferable to present it as a pharmaceutical formulation. The formulation comprises the active ingredient as above defined, together with one or more pharmaceutically acceptable excipients thereof and optionally other therapeutic ingredients. The excipient(s) must be xe2x80x9cacceptablexe2x80x9d in the sense of being compatible with the other ingredients of the formulation and not deleterious to the recipient thereof.
The formulations include those suitable for oral administration and may conveniently be presented in unit dosage form prepared by any of the methods well known in the art of pharmacy. Such methods include the step of bringing into association the active ingredient with the carrier which constitutes one or more accessory ingredients. In general, the formulations are prepared by uniformly and intimately bringing in to association the active ingredient with liquid carriers or finely divided solid carriers or both, and then, if necessary, shaping the product.
Formulations of the present invention suitable for oral administration may be presented as discrete units such as capsules, cachets, sachets of granules or tablets (such as a swallowable, dispersible or chewable tablet) each containing a predetermined amount of the active ingredient; as a powder or granules; as a solution or a suspension in an aqueous liquid or a non-aqueous liquid; or as an oil-in-water liquid emulsion or a water-in-oil liquid emulsion. The active ingredient may also be presented as a bolus, electuary or paste.
A tablet may be made by compression or moulding optionally with one or more accessory ingredients. Compressed tablets may be prepared by compressing in a suitable machine the active ingredient in a free-flowing form such as a powder or granules, optionally mixed with a binder, lubricant, inert diluent, preservative, surface active or dispersing agent. Moulded tablets may be made by moulding in a suitable machine a mixture of the powdered compound moistened with an inert liquid diluent. The tablets may optionally be coated or scored any may be formulated so as to provide slow or controlled release of the active ingredient therein.
The active ingredient may also be presented in a formulation comprising micrometer- or nanometer-size particles of active ingredient, which formulation may contain other pharmaceutical agents and may optionally be converted to solid form.
Preferred unit dosage formulations are those containing a daily dose or unit daily sub-dose (as herein above recited) or an appropriate fraction thereof, of the active ingredient.
It should be understood that in addition to the ingredients particularly mentioned above the formulation of this invention may include other agents conventional in the art having regard to the type of formulation in question, for example those suitable for oral administration may include flavoring agents or taste masking agents.
It will be further understood that the compound of formula (I) may be combined with one or more other HIV anti-viral agents, for example Reverse Transcriptase Inhibitors (RTIs), Non Nucleoside Reverse Transcriptase Inhibitor (NNRTIs), and other HIV protease inhibitors.
Examples of suitable RTIs include zidovudine, didanosine (ddI), zalcitabine (ddC), stavudine (d4T), abacavir, iamivuidine (3TC) and FTC.
Examples of suitable NNRTIs include HEPT, TIBO derivatives, atevirdine, L-ofloxacin, L-697,639, L-697-661, nevirapine (BI-RG-587), loviride (xcex1-APA), delavuridine (BHAP), phosphonoformic acid, benzodiazepinones, dipyridodiazepinones, 2-pyridones, bis(heteroaryl)piperazines, 6-substituted pyrimidines, imidazopyridazines, 1,4-dihydro-2H-3,1-benzoxazin-2-ones, such as (xe2x88x92)-6-chloro4-cyclopropylethynyl-4-trifluoromethyl-1,4-dihydro-2H-3,1-benzoxazin-2-one (L-743,726 or DMP-266), and quinoxalines, such as isopropyl (2S)-7-fluoro-3,4-dihydro-2-ethyl-3-oxo-1-(2H)-quinoxalinecarboxylate (HBY 1293) or HBY 097.
Examples of suitable HIV protease inhibitors include those disclosed in WO 94/05639, WO 95/24385, WO 94/13629, WO 92/16501, WO 95/16688, WO/US94/13085, WO/US94/12562, US 93/59038, EP 541168, WO 94/14436, WO 95/09843, WO 95/32185, WO 94/15906, WO 94/15608, WO 94/04492, WO 92/08701, WO 95/32185, and U.S. Pat. No. 5,256,783, in particular (S)-N-((.alpha.S)-((1R)-2-((3S,4xcex1S,8xcex1S)-3-(tert-Butylcarbamoyl)octahydro-2(1H)-isoquinolyl)-1-hydroxyethyl)phenethyl)-2-quinaldaminosuccinamide monomethanesulfonate (saquinavir), N-(2(R)-Hydroxy-1(S)indanyl)-2(R)-(phenylmethyl)4(S)-hydroxy-5-[1-[4-(3-pyridylmethyl)-2(S)-(N-tert-butylcarbamoyl)piperazinyl]]pentaneamide (indinavir), 10-hydroxy-2-methyl-5-(1-methylethyl)-1-[2-(1-methylethyl)4-thiazolyl]-3,6-dioxo-8,11-bis(phenylmethyl)-2,4,7,12-tetraazatridecan-13-oic acid, 5-thiazolylmethyl ester (ritonavir), (N-(1,1-dimethyl)decahydro-2-[2-hydroxy-3-[(3-hydroxy-2-methylbenzoyl)amino]4-(phenylthio)butyl]-3-isoquinolinecarboxamide monomethanesulfonate (nelfinavir), and related compounds.
The compound of formula (I) and combinations thereof with RTIs, NNRTIs and/or HIV protease inhibitors are especially useful for the treatment of AIDS and related clinical conditions such as AIDS related complex (ARC), progressive generalized lymphadenopathy (PGL), Kaposi""s sarcoma, thrombocytopenic purpura, AIDS-related neurological conditions such as AIDS dementia complex, multiple sclerosis or tropical paraperesis, and also anti-HIV antibody-positive and HIV-positive conditions, including such conditions in asymptomatic patients.